Treating hydrocarbon fluids



. 17; 1946. J. c. MUNDAY TREATING H/YDROCARBON FLUIDS Filed Oct. 14,1943 Patented Dec. 17, 1946 UNITED STATES PATENT oFElcE 2,412,645TREATING mmRocAaBoN FLUms John C. Monday, Cranford,-N. J., assigner toStandard Oil Development Company, a corporation oi' Delaware ApplicationOctober 14, 1943, Serial No. 506,169

v naphtha to produce aviation gasoline. My present invention is animprovement over such other processes. y

According to my invention, a relatively heavy hydrocarbon, such as gasoil, is cracked in the presence'of a catalyst at a relatively hightemperature and from the cracked products are separated a light naphthafraction, a heavy naphtha fraction, and a heavier oil'fraction. Thelight naphtha fraction is alkylated with isobutane, and

'the heavy naphtha fraction is 'subjected to 'a catalytic recrackingoperation. The products from these steps are then fractionated toseparate light hydrocarbon fractions boiling in the aviation gasolinerange, and the fractions are blended to produce a finished aviationgasoline of high stability, high octane number, high susceptibility totetraethyl lead and high rich mixture performance. Furthermore, theethylene and butylenes produced in the cracking and recracking steps mayalso. be subjected to alkylation with isobutane since the productalkylate is of high quality and augments the yield of aviation gasoline.

The light fraction of the catalytically cracked naphtha which is fed tothe alkylation step should be substantially free of aromatics. The endp-oint should be chosen to exclude benzene, if an appreciable amount isformed in the cracking step. For example, the end point may be 165 or170 F. In some cases wherein the amount of benzene is very small the endpoint may be 200 or somewhat higher, but it should be borne in mind thatthe presence of even small amounts of aromatics in the alkylation feedstock results in rapid degradation of alkylation catalysts, as well asin lower yields and lower octane number products. This will be evidentfrom the following Examples 1, 1A and 1B, Example 1 showin-g mypreferred alkylation step and EX- amples 1A and 1B showing poorerresults when selecting improper fractions.

Example 1 A Sil-150 F. fraction containing no aromatics fromcatalytically cracked gasoline was alkylated With isobutane at 45 F.employing a 10/1 isobutane/olefin ratio andI sulfuric acid catalyst in'a 1/1 acid/hydrocarbonV ratio for 30 minutes contact time in acontinuous run of 103 hours duration. An acid replacement Arate of 0.5to 0.7 pound per gallon of alkylate'was required in or- (Cl. 20o-683.4)

2 der to maintaincatalyst activity. The. yield of aviation alkylate was125% of the 60-150 F.

fraction and the A. S. T. M. octane number was 87.5. The aviation octanenumber-|-4 cc. llead per gallon was equivalent to iso-octane+0.24 cc.lead per gallon.

Example 1A y.

A 60-200 F. fraction from the same gasoline containing 8.8% aromaticswhen alkylated under the same conditions required an acid replacementrate of Y1.5-1.8 pounds per gallon of alkylate in order to maintainactivity. The yield of alkylate was 118% and` thel A. S. T. M. octanenumber was 85. Y

Example 1B If a 400 F. end point naphtha is subjected to alkylation. theyield is very low and the octane number of the product may actually belower than that of the `feed stock as a result of the absorption ofaromatics by the catalyst and the alkylation of aromatics thus formingcompounds boiling above the gasoline range.

In the alkylation step, the oleiins react With isobutane to formsaturated hydrocarbons of high clear octane number, high octane numberappreciation on the addition of tetraethyl lead,

high blending octane number, and high performance when employing richfuel/air ratios as in take-oil or under heavy loads as measured by theAFD-3C test method. Each of these factors is of prime importance in theproduction of large quantities of aviation gasoline having octanenumbers of or above. Removal or conversion of the olelns in the naphthais necessary to achieve this end, and the alkylation ofl the lightcatalytic naphtha originally containing about 40% olens lowers thebromine number from about 82 ogs/gm. to less than l.

In the catalytic recracking step, also, olens are converted. so that theblend of alkylated light naphtha and atalytically r'ecracked heavynaphtha has a low bromine number and low acid heat and easily passesspecications. Since in the recracking of the heavy naphtha lowerboilingolens are produced, in a preferred modiiication of my process thelight naphtha produced in the recracking step is passedto the alkylationunit along with the light naphtha produced in the catalytic cracking. Inthis manner there is produced an aviation gasoline of quite low olencontent and very high quality.

Apparently the oleiin content is reduced in the catalytic recrackingstep partly by polymerization and partly by hydrogenation throughhydrogen exchange with naphthene hydrocarbons. The recracking causes asharp reduction in the .amounts of naphthenes and paralns present,particularly in the high boiling portions which are very high inaromatic content.

3 The heavy fractionof the catalytically cracked naphtha which issubjected to catalytic recracking must likewise be a selected fractionif high yields of high octane number aviation gasoline are to berealized, as shown by the following examples. Example 2C shows improvedyields obtained when catalytically recracking a selected heavy naphthafraction, whereas Examples 2,12A and 2B show that best results are notobtained with improperly selected fractions.

Example 2 A 'l0-410 F. naphtha produced by catalytic cracking at atemperature lin the range 925-975 F. with powdered syntheticsilicaalumina gel was recracked at 900 F. with the same catalyst and theproduct was fractionated.

The yield of 335 F. end point aviation base stock.

exclusive of pentane was 46.8% and the yield of pentane was 25.9%. Theaviation octane number+4 cc. tetraethyl lead per gallon of the feed.

stock to recracking was 88.7 while that of the depentanized aviationbase product was 94.2.

Example 2A A 11o-220? F. fraction of the same gasoline as employed inExample 2 was recracked under the same' conditions. The yield ofaviation gasoline base exclusive of pentane was 58% and the yield ofpentane was 14%, while aviation octane numbers+4 cc. lead of the feedandofthe depentanized aviation base product were86.4 and y 92.6,respectively.

V A' Example 2B i a' A 11G-289 F.

employed in Example 2 was recrackedunder-the same conditions, and.yields `of 61% vof dac-'.-

pentanized aviation' base and 11.3% of 'pentane were obtained. The feedhadan aviation octane number-F4 cc. lead of 88, while that of thedepentanizeal aviation b ase product was 92.5.

Example 2C A 220410 F. fraction4 of the gasoline employed f in Example 2was recracke'd'under the same conditions. The feed' stock .contained38.2% ,of

material boiling in the .aviation gasoline range below 3 35" F. Theyield ci depentanizedaviation base was 5,8%; the pentaneyield being4.4%, and

the yield of C4 hydrocarbons being 5.5%. Whereas .the aviation octane.number-r4 cc. leadof the feedstock was 87, that lof the depentanizedaviation base product was' 98.2.' It has Abeen foundthat ,thefractionofa catalytically cracked gasoline boilingbetween about 160 or170v F. and-"about 220 F. has va fraction of the same gasolineas' Aspointed out'above, the yield and quality of the aviation gasoline maybeaugmented by alkylation of the ethylene and butylenes produced bycracking and recracking with the isobutane produced by cracking andrecracking. In view of the requirements of normal butene and isobutyleneas feedstocks 4in synthetic rubber production, it may be desirablevto``alkylate only the ethylene at the present time.V The ethyleneshould be alkylated with isobutane in a separate unit not in thepresence of sulfuric. acid catalyst but in the presence ofa halidecatalyst, such as aluminum chloride or bromide, employing about 3/1v to.5/1 isobutane-ethylene ratio at 100-150 F. and 250-350 lbs./sq. in.pressure. The product contains 'I0-85% of Ce hydrocarbons, predominantlyv2,3-dimethyl butane'which has a very high rich mixturerating on theAFD-3C y scale.

The ethylene alkylate, or only the Cs fraction therefrom, is blendedwith the aviation fractions produced by alkylation of the lightcatalytic naphtha and by recracking the'heavy fraction of thecatalyticnaphtha. When operating sol as to alkylate ethylene and C4l oleiins aswell as thelight catalytic naphtha, the yield of finished high qualityaviation gasoline'is more than 100% based on' the original catalyticnaphtha.

In contrast to ethylene alkylation, either the Vnormal butenes orisobutylene or both can be alkylated with isobutane in-the presence ofsulfuric acidcatalyst with good results, and it is preferred 'to dothissimultaneously and in the same unit as employed in the alkylation ofthe light naphtha fractions.

In the drawing, the figure represents one form of apparatus which may beused to practice my process.

low 'octane number, fory example, about 84 aviation+4 cc. lead, and thatrecracking improves it lonly slightly, for example,to about 88. It isgenerally preferred to discard this'fraction, which may amount to 10 or12% of the catalytic gasoline, and to use it in automotive fuels. When'a discarding this fraction the charge'to the alkylation unit isabout.48% of the catalytic gasoline exclusive of C4 hydrocarbons, andthe 220410 F. fraction charged to the recracking step amounts to about40% of the catalytic gasoline. t

As shown in VExample 1, the yield Vfrom alkylation is 125%.of thechargeor 60% based on the catalytic gasoline, and this alkylate has anaviation octane number-i4 cc. lead greaterthan 100 (isooctane+0.24 cc.lead) As shown in Example 2C, the yield of depentanized aviation basestock from the recracking step is 58% of the charge, or 23% based onthe` catalytic gasoline.

vReferring now to the drawing, the reference character'lll designatesaline through which the hydrocarbon oilfeed stock is introduced to thesystem. For example, the feed` may comprise gas .oil vapors4 orvotherrelativelyheavy vaporv ized petroleum stock.v

catalyst, it is also possible to startv with a partly 1 When4 usingpowdered preheated liquid stock andto supply the heat of vaporizationand conversion by contact with a suilicient quantity of hot catalyst.The hydrocarbons are cracked at atmospheric pressure or thereab'outsat'a temperature of about 900 F. to

1000. F., preferably about-975 F. when cracking a relatively heavy gasoil having an A. P. I.

gravityof 25430"v and a mid-boiling point of about 60G-750 F.

Thecatalyst may be 'any suitable cracking catalyst, such as syntheticsilica alumina gel, synthetic silica magnesia gel, acid-treatedbentonites, etc. For the preparation of aviation gasoline and relativelylarge amounts of oleiins, it is preferred to use the synthetic silicaalumina gel. The preparation of such a catalyst is well known and is,not described here.l Instead of vusing powdered catalyst, it is withinthe contemplation of my invention to use larger particles of amaca meshor finer.

The hydrocarbon feed stock is passed through line I0 into the bottomportion of a reaction vessel I8 which contains dry powdered catalyst atreaction temperature. The velocity of the vapors passing throughreactionvessel I8 is controlled so that the catalyst particles remain in thevessel for a much longer period of time than the vapors, and preferablysuch that a relatively densev layer of catalyst is present in the lowerportion ofthe vessel. Suitable velocities lie in the range from 0.5 to10, preferablyvl to 3, linear feet per'second when employing 200-400mesh catalyst having a density when freely settled of from 35 to 60lbs/cu. ft.' Under these conditions the relatively dense catalyst phasehas a density of the order of to 30 lbs./cu. ft. The relatively densecatalyst phase is aerated by the rising vapors and has the appearance ofa violently boiling liquid, and possesses properties of liquids such asfluidity, the ability to exert hydrostatic pressure and a level ormeniscusY which is especially noticeable when low vapor velocities areemployed. Also, when employing relatively low velocities, such as from0.5 to 2 ft. per second, the carry-over of catalyst by the crackedproduots is very small, of the order of 0.003-0.01

lbs/cu. ft. of vapors.

The cracked products leave the top of the reaction vessel I8 throughline 22, after lpassing through cyclone separator 24 where entrained 'iniixed bed operation. Preferably the .powdered tower 32 through line-38and are subjected to l fractionating and/or scrubbing operations toseparate fractions rich in ethylene and in C4 hydrocarbons. Theseoperations, which are well known and need not be described in detailhere, are indicated on thedrawing by numeral 43. Light gases passoverhead through line 44. A C3 fraction is withdrawn through line 45.The septhe upper portion of vessel I8. Other forms of separating meansmay be used. Separated catalyst is returned to the reaction zone properthrough linie 25. During the conversion operation the powdered catalystbecomes contaminated with coke or carbonaceous material and lt isnecessary to regenerate the catalyst in any known manner,l preferably byburning with air or oxygen-containing gas at about 1000-1l00"l F. toVremove the carbonaceous deposit. Catalyst for regeneration is withdrawnfrom reaction vessel I8 through line 26 in a luidized condition and ispassed to a regenerator (not shown) Ywhich may be similar inconstruction to vessel i8. Hot regenerated-catalyst is returned to lineI0 and to the reactor through line 28 at a suiiicient rate to maintainreactor` temperature and catalyst activity at the desired levels, vandif liquid feed stock is being supplied to the reaction, to absorb orvaporize the liquid cornpletely. The weight ratio of catalyst to oil.employed is generally above 3, for example, from 5 to 20.

While I have shown only one cyclone separator on the drawing, it is tobe understood that more than one cyclone separator may be used in series4arated C4 fraction withdrawn through' line 45 contains isobutylenewhich is useful in the production of synthetic'rubber and theisobutylene may be recovered by scrubbing with acid. The acid used ispreferably sulfuric acid having a concentration of about 65% by weight.The C4 fraction is introduced into the bottom portion of an acidscrubbing vessel 48, the acid is introduced at the top through line 52,and the acid extract is removed through line 53. In the scrubbing vessel48 the temperature of the sulfuric acid is about 75 F. The isobutyleneis recovered from the`acid by treating with steam, thus raising thetemperature to about 250 F. and lowering the acid concentration toLl045%. Isobutylene and di-isobutylene are ashed overhead and the latteris cracked to form isobutylene. If isobutylene is not desired forsynthetic rubber, the entire C4 cut is by-passed around acidv scrubber48 through line 54 to line 56 leading to alkylation unit 51.

, 'I'he rest of the C4 fraction containing isobutane and butenes leavesscrubber 48 through the line and is mixed with a light naphtha fractionintroduced through line 58. This light naphtha fraction is withdrawnfrom the upper part of fractionating tower 32 wherein the catalyticallycracked products -are fractionated. The light naphtha fraction collectson trap-out tray 62 in the fractionating tower 32 and is passed throughline 58 by pump 64. The light naphtha fraction contains olens andparalins, but as mentioned above, should be substantially free ofaromatics. The light naphtha fraction has a boiling range of about 60 toabout 170 F. or 200 F. .l

The mixture of the light cracked naphtha and the C4 fraction is passedthrough line 58 to the alkylation unit or reactor 51 wherein the olensare alkylated with isobutane to transform the olefins to branchedparafns. Any suitable alkylation -catalyst is used, such as sulfuricacid, boron fluoride-water, hydrogen fluoride, etc. Where sulfuric acidis used, the titratable acidity of the acid is maintained above about82%, preferably at about 85-90%, by continuous .replacement with 94-98%acid. The temperature during alkylation is preferably in the rangeli5`80"` F. The ratio of isobutane to oleflns in the feed is generallymaintained at 3/1ior higher by reto effect a better separation ofpowdered catalyst I Vhydrocarbons leave the top of the fractionatingcycling isobutane separated from the products, and the vinstantaneousisoparaiiin/olen ratio in the reactor is maintained considerably higher,for

example, 30/1 or 100/1 or'greater, by recycling,

products which are low in olens to the inlet of the reactor.

The acid for the alkylation unit is introduced through line 'l2 andspent acid sludge is withdrawn through line 'M The products ofalkylation are passed through line 76 into a second fractionating towerI8 for separating the desired light hydrocarbons boiling in the aviationgasoline range from higher boiling constituents. The

light hydrocarbon constituents lpass overhead through line 82, arepartially condensed in condenser 84, and passed to a separator 86wherein gases are separated from liquid. The gases comprising C4 andlighter pass overhead through line I8 -and are fractionated in equipment(not shown) fraction is withdrawn froml separator 86 as a liquid throughline 82. This light fraction boils up to the end point of the desiredaviation gasoline, generally 30D-330 F. and is substantially free ofolens. Higher boiling constituents are.with drawn from the bottom of thefractionator 18 through line 94. These higher boiling constituents maybe addedtogordinary motor gasoline.

As mentioned earlier, it is frequently desirable to alkylate theethylene produced in the cracking and recracking operations withisobutane. To this end the ethylene separated in fractionating andscrubbing equipment 43 and which may have a purity from`25 to 80% ispassed through line 85 to an alkylation unit 86 where it isalkylatedwith isohutanel in the presence of aluminum ch1o' ride. Isobutane isintroduced through line 91.

`.The isobutane may come from cracked products v in my process or fromanextraneous source. The conditions of operation are similar to thoseemboiling above the aviation gasoline range reduces their boiling pointsand thereby increases the yield of aviation naphtha.

The'vaporous reaction products pass overhead from reactor through line|24 to a third of the heavy naphtha fraction additional amounts ofisobutane are formed together with other valployed in alkylation unitlexcept that the temperatureis higher (1D0-150 F.).andthe pressureV maybe 250K-350 'lha/sq. in.1The `products are passed through'1ine98`intofractionatorJB along with the products from 'alkylationunit v51.

Returning now to the first-mentionedl fractionating tower 32, thecatalytically crackedproduable light olenic hydrocarbons. These lighthydrocarbons are withdrawn from the top of the fractionating tower |34through line |36 and are .combined withthe gaseous products leaving therst fractionator 32 through line 36. This mixture is then treated toseparate isobutane and olefins from the other gases vfor use in thealkylation units 51 and 86.

Ihe reaction products in the iractionator |34 are fractionated toseparate an aviation naphtha fraction vwhich collects on trap-out tray|40. Thisfraction is relatively heavy, boiling for ,the most'partbetween about 190 and 335 F. and contains high quality constituentsfor aviation gasoline. The aromatic content of the naphtha is very high,lparticularly of the 22o-335 F. fraction which mayfbe v8090% aromaticsor higher.

' The naphtha fraction is withdrawn from trapucts are furtherfractionated to separate aheavyf naphtha fraction which is .withdrawnvfrom trapout tray |02 through line |04 by pump |06. Ihis higher, andcontains olens, parafilns, aromatics andnaphthenes. vThe paraflinsandsome of the .oleiins are ofr poor- Isome of the alkylated aromaticshavea high boil-l ing point and. it i s desirable to break oft'part of thechains of the alkylated aromatics to reduce their boiling point.

To improve the quality ofthe heavynaphtha u :outtray |40through line |42and is mixed with the, light .alkylate fraction withdrawn throughlinef92 and the mixture is Withdrawn through line V| 44 as 'an aviationgasoline.y The addition of 4 or 4.5`cc.-` of tetraethyl lead per gallonandadjustment of 'the vapor pressure by adjustment of heavy naphthafraction has'an initial' boiling point from about 170 F. to about 4220"F. and may have an end point of 350 or -400 lor somewhat 1theisopentanecontent of the gasoline produces -a finished aviation gasoline of highstability and high octane numberby both the aviation octane number 'andthe AFD-3C methods of testing.

A heavier `fraction collects on lower trap-out tray |46'in.th efractionating tower |34 and this fraction is withdrawn through line |48.This heavier fraction may be added to motor gasoline. In a preferredmodication, a light fraction of 'the recrackedproducts, and whichcontains olefraction, it is passed through a second catalytic crackingoperation in reactorl'll. Therecracking unit is` operated in the samemanner as the cracking unit described earlier, employing vpow.-v

dered cracking catalystof thesame or different composition.' Syntheticsilica-alumina gel is a` preferred catalyst. The temperature ofoperation is generally slightly lower than in cracking,

V "for example, '700'tof950 F., particularly if the cracking unit is`operated to give -high conversions. With cracking conversions of theorder of -80%, 900 F. is a suitable temperature for Withdrawn from thereactor through line |'|2, re-

generated and returned through line I4. A cy-i clone separator H6 andreturn pipe |'l8 are used.-`

A common regeneratoris preferably employed for passing to the reactionzone ||0 remain as aromatics, but de-alkylation of alkylated aromaticsand modifications may be 'made without depart ing' from'the spirit of myinvention.

II claim:

` A methodbt 'producing aviation 'gasoline which 1 recraclnng. A streamof catalyst is continuously G0- boiling frange o f about Gti-165 F., anintermecomprises. separating a catalytically Acrackedriaphthaintoalightlnaphtha fraction having a diate naphthafractionhaving a boiling range ot about ITG-'220 F.,'and a heavy naphthafraction having a boiling range of about 22o-410 F., a1-

kylating the separated light naphtha fraction with isobutane totransform olens to branched chain hydrocarbons.' discarding theseparated in-

